Re: System headers with clang?

On 2011-10-09 19:32, Larry Rosenman wrote:
> I had gotten a PR about sysutils/lsof not compiling with clang.  I had
> Vic Abell check it out, and the problem is NOT with lsof per se, but
> with the system headers.
>
> Is there a project afoot to update the system headers to make them clang
> compilable?

The problem isn't that clang can't compile the system headers, but
normally these don't get included from userspace.  And they certainly
won't work as expected when you define _KERNEL in userspace, as the lsof
port foolishly does.  It probably can't be avoided in such a tool, though.


...
> In file included from ckkv.c:43:
> In file included from ./../lsof.h:195:
> In file included from ./../dlsof.h:190:
> In file included from /usr/src/sys/ufs/ufs/ufsmount.h:36:
> /usr/src/sys/sys/buf.h:388:2: warning: implicit declaration of function 'KASSERT' is invalid in C99
> [-Wimplicit-function-declaration]
>           KASSERT(bp->b_bufobj != NULL, ("bwrite: no bufobj bp=%p", bp));
>           ^
> /usr/src/sys/sys/buf.h:388:33: warning: expression result unused [-Wunused-value]
>           KASSERT(bp->b_bufobj != NULL, ("bwrite: no bufobj bp=%p", bp));
>                                          ^~~~~~~~~~~~~~~~~~~~~~~~~

These are more or less harmless warnings, as long as nobody calls a
function that uses KASSERT.  They occur because lsof's headers don't
include <sys/param.h> and <sys/systm.h> before <sys/ufs/ufs/ufsmount.h>.

...
> In file included from ckkv.c:43:
> In file included from ./../lsof.h:195:
> In file included from ./../dlsof.h:432:
> In file included from /usr/include/string.h:45:
> /usr/include/strings.h:47:6: error: conflicting types for '__builtin_ffs'
> int      ffs(int) __pure2;
>            ^
> /usr/include/machine/cpufunc.h:140:24: note: expanded from:
> #define        ffs(x)  __builtin_ffs(x)
>                          ^
> /usr/include/strings.h:47:6: note: '__builtin_ffs' is a builtin with type 'int (unsigned int)'

This is because the amd64 system headers redefine ffs to __builtin_ffs,
after which it conflicts with the declaration in /usr/include/strings.h.
On i386, ffs is not redefined, but I have no idea why.

In any case, gcc does not complain about the incompatible redeclaration,
which may be a bug, or just stupid luck, depending on your POV. :)

I've attached a fix for the lsof port, which also makes it build on
10.0-CURRENT (this was easy to fix here, as lsof uses its own
hand-rolled configuration script).  Let me know if it works for you.